import java.util.Arrays;

public class No007 {
    /**
     * 输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。
     * 假设输入的前序遍历和中序遍历的结果中都不含重复的数字。
     * 例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。
     */
    public static void main(String[] args) {
        TreeNode treeNode = reConstructBinaryTree(new int[]{1, 2, 4, 7, 3, 5, 6, 8}, new int[]{4, 7, 2, 1, 5, 3, 8, 6});
        assert treeNode != null;
        System.out.println(treeNode.left);
        System.out.println(treeNode.right);
    }

    public static TreeNode reConstructBinaryTree(int[] pre, int[] in) {
        if (pre.length == 0 || in.length == 0) {
            return null;
        }
        int root = pre[0];                  //前序遍历的0索引为根
        TreeNode treeNode = new TreeNode(root);
        for (int i = 0; i < in.length; i++) {
            if (in[i] == root) {            //找到中序遍历的根
                treeNode.left = reConstructBinaryTree(Arrays.copyOfRange(pre, 1, i + 1), Arrays.copyOfRange(in, 0, i));
                treeNode.right = reConstructBinaryTree(Arrays.copyOfRange(pre, i + 1, pre.length), Arrays.copyOfRange(in, i + 1, in.length));
                break;
            }
        }
        return treeNode;
    }

    public static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int x) {
            val = x;
        }

        @Override
        public String toString() {
            return "TreeNode{" +
                    "val=" + val +
                    ", left=" + left +
                    ", right=" + right +
                    '}';
        }
    }
}
